Direct Shear Tests on Intact Rock, How to Determine Normal Forces to Apply?

[Lets get dirty]

I need the lab to run ASTM 5607 on a few rock samples from a project.

One sample will be from 65' down hole, with 15' of rock above it, followed by 50' of very stiff to hard clay and some dense silt layers. Any advice on determining the normal forces to apply during the test? This is not for a foundation, potentially a small utility "tunnel" will be drilled through the rock.

 

[EireChch]

Interesting, I have never actually encountered anyone doing direct shear on rock samples.

For direct shear box testing on SAND we do 3 pressures, one at half your effective overburden, one at your effective overburden and one at 2 times your effective overburden.

I cant see why you would need to do anything different?

 

[GeoEnvGuy]

For direct shear box testing on SAND we do 3 pressures, one at half your effective overburden, one at your effective overburden and one at 2 times your effective overburden.

I cant see why you would need to do anything different?

If this is a large earthworks project consider the proposed effective stress whether its higher or lower.